Three natural ingredients are key to an Earth that runs on sustainable fuel

When it comes to creating clean, sustainable energy all day every day, plants have it down.

Using sunlight and water to create their own energy, plant photosynthesis is still infinitely more sustainable and efficient than even our best solar technology.

Solar panels have been able to get us close to harnessing the Sun's energy for our own fuel needs, but the cost of upgrading existing infrastructure to run on solar power — as well as technological challenges — have stood in the way of a sci-fi future with solar-powered transportation.

But scientists haven't given up hope on this sunlit future. Now, researchers have designed a new, wireless device that can synthesize carbon dioxide, sunlight, and water to create a multi-use, carbon-neutral fuel. The flexibility of this energy creation could make it a good fit into the existing energy infrastructure and a feasible alternative to fossil fuels.

The researchers were able to yield nearly 100 percent fuel from this reaction without any wasteful byproducts.

In a new study published Monday in the journal Nature Energy, a team of chemists from the UK and Japan describe a wireless device for solar energy-harvesting that uses just water, CO2, and sunlight to produce formic acid — a type of fuel that can either be used directly or converted into hydrogen.

"Sometimes things don't work as well as you expected, but this was a rare case where it actually worked better."

The researchers explain that the approach is similar to work published by the UK arm of the team in 2019. The previous research focused on creating "artificial leaves" that used tiny solar cells to absorb photons for energy. An important difference in this study, the authors say, is that it's even more simplistic, using a "photosheet" instead of individual solar cells to spark this chemical transformation.

Photosheets are made from semiconductor powders and can be manufactured on a mass scale, making them ideal for cost-effective scaling of the technology, the authors say.

This new approach is also more efficient in producing fuel than expected, overcoming a major challenge for the field, says Qian Wang, the study's first author and chemist at the University of Cambridge.

"It's been difficult to achieve artificial photosynthesis with a high degree of selectivity, so that you're converting as much of the sunlight as possible into the fuel you want, rather than be left with a lot of waste," Wang said in a statement.

The team's device is just under eight square inches in size, but, when exposed to sunlight, CO2, and water, it was able to spark a reaction that created 97 percent formate — a derivation of formic acid — and barely any byproducts. This means that the photosheet gives an incredibly high return on investment.

While the researchers had hoped their device would perform well, this performance is even better than they expected.

"Sometimes things don't work as well as you expected, but this was a rare case where it actually worked better," Wang said.

Erwin Reisner, the study's senior author and professor at the University of Cambridge, said that the new approach would make it easy to store the formic acid for later use, either as hydrogen, or converted from solution into a different fuel type. Unlike solar power, which is typically used to generate electricity, an approach like this may be able to produce liquid fuels to power things like airplanes or cars that traditionally run on fossil fuels.

The researchers are still working to improve the efficiency of their approach and to explore other chemical catalysts before they plan to take it to market, but a wireless solution like this could one day be scaled up to create sustainable and practical solar-energy production, Reisner said. Such a device might be used to create wireless energy farms in communities will little access to an electric grid.

Abstract: Harvesting solar energy to convert CO2 into chemical fuels is a promising technology to curtail the growing atmospheric CO2 levels and alleviate the global dependence on fossil fuels; however, the assembly of efficient and robust systems for the selective photoconversion of CO2 without sacrificial reagents and external bias remains a challenge. Here we present a photocatalyst sheet that converts CO2 and H2O into formate and O2 as a potentially scalable technology for CO2 utilization. This technology integrates lanthanum- and rhodium-doped SrTiO3 (SrTiO3:La,Rh) and molybdenum-doped BiVO4 (BiVO4:Mo) light absorbers modified by phosphonated Co(ii) bis(terpyridine) and RuO2 catalysts onto a gold layer. The monolithic device provides a solar-to-formate conversion efficiency of 0.08 ± 0.01% with a selectivity for formate of 97 ± 3%. As the device operates wirelessly and uses water as an electron donor, it offers a versatile strategy toward scalable and sustainable CO2 reduction using molecular-based hybrid photocatalysts.